In the Meditations, Descartes attempted to set a foundation for knowledge. Critics say that his argument at one point is circular. In arguing for the veracity of clear and distinct ideas he assumes the existence of God and in arguing for the existence of God he assumes the veracity of clear and distinct ideas. But there is no textual evidence for the so-called Cartesian Circle, according to Newman and Nelson's "Circumventing Cartesian Circles," (1999) summarized here. Instead, the real form of Descartes' dialectic is analogous to the theodicy or the problem of evil. And is an illustration that "one man's ponens is another man's tollens." Cool!